Electrolytic cleaning process



Patented May 13, 1947 UNITED STATES PATENT OFFICE ELECTROLYTIC CLEANINGv PROCESS I Richard w. Kingerley, Jr., Lakewood, Ohio, as

signor to E. I. dn Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March, 5, 1943, Serial No. 478,115

7 Claims. (Cl. 204-145) This invention relates to the removal of mineraloils from metallic surfaces and is more particularly-dii ected to processes whereby mineral oil is removed from metallic surfaces byelectrocleaning in a sodium silicate solution with an SiOu/NazO ratio from about 1.9 to 2.4

At present, the electrocleaning of steel strips is concerned mainly with cleaning the steel coming from the cold rolling operation. The mate--. rial to be cleaned from the strips is essentially the lubricant in the cold rolling operation, to-

- gether with any pickling smut left on the steel prior to cold rolling.

In the electrocleaning operation, the strip is passed through a long tank filled with an alkaline detergent. The steel strip may be made the cathode, the anode, or a central conductor between the alternating cathodes and anodes; Usually a current density of 25 to 50 amps./ft. is applied. Temperature is maintained near the boiling point. The strip is passed through this cleaning bath at speeds ranging from 500 to 3000 ftJmin. Application of the electric current is useful in securing faster cleaning and a higher quality of cleaning than would be possible without it.

The alkaline detergents used as the electrolytes in the electrocleaning tanks are quite important to the success of the operation. At the present time, the most widely used detergent is sodium orthosilicate. In the past, the cold rolling lubricants which had to be removed in the electrocleaning operation have consisted wholly or in part of palm oil. in removing the palm oil from the sheet is probably largely chemical, that is, saponification of the palm oil. This is justification for using such a highly alkaline material as sodium orthosilicate.

Efforts to-remove mineral oil from steel strips by electrochemical means have not been too successful. ,Generally, inordinately long cleaning times are required and it has been very diflicult to secure a sheet free from water break." is one of the reasons why it has not been possible to utilize cheap and readily available mineral oil as the lubricant for the cold rolling operation in place of palm oil.

It is an object of this invention ,to provide an electrocleaning detergent process for the removal of mineral oil from steel surfaces. It is a I further object to provide processes which may easily and economically be used to remove mineral oil from steel surfaces as quickly and'as completely as saponifiable oils have been removed The action of the detergent This 2 in the past. It is a. still furtherobject to provide processes by means of which there may beobtained a protective foam blanket on top of an electrocleaning solution. It is a still further object to provide processes employing certain modified mineral oils in combination with certain detergent compositions so that the mineral oils may be removed quickly and effectively. Still further objects will become apparent hereinafter.

The foregoing and other objects of this invention are attained byemploying as a detergent in an electrocleaning bath sodium silicate having an SlOa/NazO weight ratiofrom about 1.9 to 2.4. A non-ionic foaming agent is preferably included in the electrocleaning bath to give a surface foam. The mineral oil is preferably modified by the inclusion of very small amounts of an oll-dispersible sulfonated vegetable or animal oil such as sulfonated castor oil, a material for increasing film strength such as tricresyl phosphate, and on oilsoluble surface active agent such as Lorol phosphate.

It is preferred to use electrocleaning processes of the present invention for the removal of a mineral oil which contains modifying agents as more particularly described hereinafter. The mineral oil which comprises the major proportion of the lubricant for the cold reduction of steel may be any suitable grade of mineral oils from a fairly light mineral oil to so-called heavy engine oils depending'upon the specific conditions of the rolling mill practice in accordance reaction between the sperm oil and sulfur occurs, as described in The Chemical Analysis'of Oils, Fats, and Waxes," by J. Lewkowitsch, p. 14 of second edition, published 1898 by Macmillan & Company, London.

Most of the agents useful for increasing the film strength of a mineral oil increase the time required for-cleaning the oil from steel surfaces. However tricresyl phosphate produces the desired increase in film strength without adversely affecting the cleaning time and it is accordingly preferred to use tricresyl phosphate. An agent for increasing film strength may be used in amounts comparable to those heretofore employed while more specifically it may be indicated that from about 0.5 to 2 percent by weight of tricresyl phosphate may be used.

A material for increasing the spreading characteristics of mineral oil is preferably included in an oil to be removed with the detergents of the present invention. The art is already aware of a number of oil-soluble surface-active agents that can be used to improve the spreading characteristics of oil in the presence of water. Typical of the oil-soluble, surface-active agents for improving the spreading characteristics of oil are: mono, di, and tri Lorol phosphates and commercial mixtures of them prepared by esterifying with phosphoric acid the mixture of alcohols known as Lorol, which is a mixture of primary normal aliphatic alcohols of eight to sixteen carbon atoms which are obtained by free tionation of the alcohols resulting from the reduction of cocoanut and/or palm kernel oils; aryl amine lauryl sulfates that is, products of the type formed by sulfating lauryl alcohol with concentrated sulfuric acid and neutralizing the resultant sulfate with anaryl amine, and having the formula AI.NH2HSO4CH2(CH2)10CH3; alkyl sulfates such as those shown in Tisdale et al. 2,128,973; and Tween 81, a sorbitan monooleate polyoxyalkylene derivative.

While any of the oil-soluble, surface-active agents may be employed most of these materials increase the time required for removing the oil from the steel. A preferred material for this use, therefore, is Lorol phosphate which has been found to have little adverse effect at the 0.05 to 0.3 percent by weight of the total lubricant.

Modified mineral oil lubricants to be removed from steel by the processesof the present in- 'vention preferably contain an oil-dispersible Sulfonated fish oil Sulfonated lard oil Sulfonated sperm oil Sulfonated soya bean oil Sulfonated peanut oil- Sulfonated corn oil Sulfonated cotton seed oil Sulfonated castor oil A suitable sulfonated oil for use in mineral oil which is to be removed with a detergent of the ".present invention is sulfonated castor oil. By

using this in a mineral oil the time required to electroclean steel is reduced'to a minimum. In general it will be found desirable to use from about 0.2 to 0.5 percent by weight of sulfonated castor oil.

While a modified mineral oil as above described is preferably used as a lubricant in the cold reduction of steel it will be understood that similar modified oils containing sulfonated castor oil may be used on various metallic surfaces as lubricants and to prevent rusting and then may advantageously be removed quickly by electrocleaning in a detergent solution of the present invention.

The modifying agents above described are pref erably added to a mineral oil in the form of a composition made up of the modifying agents and a suitable amount of a solvent. There may be used as a solvent such materials as tetralin, toluene, and petroleum fractions ranging from light naphthas to kerosene.

The silicate detergent solutions used in a process of the present invention are made up with sodium silicate having an SiO2/Na2O Weight ratio from about 1.9 to 2.4. The silicates should .be used in sufiicient amounts to obtain a desired solution conductivity. Thus in general from about 2 to 8 ounces per gallon of such a silicate should be used.

A foaming agent is included in the silicate solution so that a foam blanket will be formed on the surface of the bath. Soap is customarily used in electrocleaning solution but even very small amounts of an ionic foaming agent is very deleterious to the detergent of this invention for the removal of mineral oils from metallic surfaces.

Accordingly there may be employed a non-ionic foaming agent. As examples of non-ionic foaming agents there may be mentioned:

Saponin Soap bark Maleic anhydride-styrene polymer Igepal C (a polyglycol ether of the type described in U. S. Patent No. 2,213,477 and having the general formula as set forth in claim 1 of that patent) NNO (hexitan partial fatty acid ester, prepared gygprocedures described in U. S. Patent 2,134,-

Span 20, 80, (sorbitan monolaureate, palmitate,

oleate) Tween 81 (sorbitan monooleate-poly-oxyalkylene derivative, prepared by effecting reaction between ethylene oxide and free hydroxyls of sorbitan monooleate) The preferred non-ionic foaming agents for use according to the present invention are maleic anhydride-styrene polymers, saponin, and certain polyalkylene oxide derivatives. The polyalkylene oxides and preferably polyethylene oxides may be unsubstituted or substituted. The substituted polyalkylene oxides such as those shown in Patents No. 1,970,578 and 2,213,477 are preferred. One such product offered on the market Igepal C has been found particularly advantageous and this is thought to be a condensed product of an alkylated phenol with ethylene oxide. The maleic anhydride-styrene polymer and related polymeric materials may be prepared as in Condo et a1. 2,286,062 and Graves 2,205,882.

The foaming agents can be used in any desired amount, the quantity of course being sufllcient to produce a foam blanket of desired thickness. In general from about 0.02 to 0.2 percent of maleic anhydride-styrene polymer, saponin, or a polyalkylene oxide will be found suillcientu While there are shown certain illustrative compositions and processes it will be understood that the invention is not to be limited thereby but that numerous modifications may be made without departing from the spirit of the invention.

The modified mineral oils described herein and modifying compositions for mineral oils are claimed in my co-pending application, Serial Number 478,114 filed March 5, 1943.

Iclaim:

1. In a process for the removal of mineral oil from a ferrous metal following cold-rolling of the metal using the oil as a lubricant the step comprising electrocleaning the metal in a silicate detergent solution comprising essentially a sodium silicate having an SiOz/NazO weight ratio from about 1.9 to 2.4, the weight ratio of total S102 to total NazO in the solution also being in the range from 1.9 to 2.4.

2. In a process for the removal of mineral oil from a ferrous metal followin cold-rolling of the metal using the oil as a lubricant the step comprising electrocleaning the metal in a silicate detergent solution comprising essentially a sodium silicate having an SiOz/NazO weight ratio from about 1.9 to 2.4 and a non-ionic foaming agent. the weight ratio of total Slo to total NazO in the solution also being in the range from 1.9 to I '35 6. In a process for employing mineral oil in the cold reduction of steel the steps comprising applying a lubricant comprising a major amount to 2.4, the weight ratio of total S10: to total; NazO in the solution also being in the range from 1.9 to 2.4.

. 4. In a process for employing a mineral oil on a ferrous metal surface the step comprising applying to the metal surface a mineral oil containing a minor amount of sulfonated castor oil a ferrous metal surface the step comprising ap- .plying to the metal surface a mineral oil containing 0.2 to 5 percent of sulfonated castor 011 subjecting the metal to cold-rolling, and then later electrocleaning the metal to remove the mineral oil in a. silicate detergent solutioncomprising essentially sodium silicate having an SiOz/NazO weight ratio from about 1.9 to 2.4, the weight ratio of total SiOz to total No.20 in the solution also being in the range from 1.9 to 2.4.

of a mineral oil which contains from about 0.2 to 0.5 percent of sulfonated castor oil, from about 0.2 to 2 percent of tricresyl phosphate, and from about 0.1 to 0.3 percent of Lorol phosphate subjecting the metalto cold-rolling, and then later removing the modified oil by electrocleaning in a silicate detergent solution comprising essentially a sodium silicate having an SiO2/Naz0 weight ratio .from about 1.9 to 2.4, the weight ratio of total S102 to total NazO in the solution also being in the range from 1.9 to 2.4.

7. In a process for employing mineral oil in the cold reduction of steel the steps comprising applying a lubricant comprising a major amount of va mineral oil which contains from about 0.2 to 0.5 percent of sulfonated castor oil, from about 0.2 to 2 percent of tricresyl phosphate, and from about 0.1 to 0.3 percent of 'Lorol phosphate subjecting the metal to cold-rolling, and then later removing the modified mineral oil by electrocleaning in a silicate detergent solution com- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,044,467 Cleveland June 16,1936 2,175,781 Riggs et a1. Oct. 10, 1939 1,531,782 Hamilton Mar. 31, 1925 2,677,389 Howes July 17, 1928 2,285,855 Downing et a1 June 9, 1942 2,325,957 Krogel Aug. 3, 1943 2,314,285 Morgan Mar. 16, 1943 1,878,096 Bamblett Sept. 20, 1932 1,935,911 Neilson Nov. 21, 1933 1,601,511 Schmutz Sept. 28, 1926 2,230,909 Riggs et al. Feb, 4, 1941 2,206,289 McDaniel Jul 2, 1940 FOREIGN PATENTS Number Country Date 525,514 Great Britain Aug. 29, 1940 OTHER REFERENCES Promi'sel, article in the Monthly Review of the American Electroplaters Society, June 1935, page 7. (Copy in Scientific Library.)

Crowe, article in Products Finishing, November 1941, pp. 56-59. (Copy in Scientific Library.)

The Metal Industry, Dec, 22, 1939, p. 526.-

Vail, Soluble Silicates in Industry (1928) p. 323. 

